Derivative Financial Instruments - Summary of the volume and fair value positions of derivative instruments (Details) $ in Millions	Sep. 30, 2020 USD ($) contract	Dec. 31, 2019 USD ($) contract
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Cash and securities pledged in the form of margin deposits	$ 63
Derivatives, Fair Value
Total asset derivatives, notional amount	793	$ 75
Total liability derivatives, notional amount	3,065	3,403
Total derivatives, notional amount	$ 3,858	$ 3,478
Total asset derivatives, number of contracts | contract	4,260	10,740
Total liability derivatives, number of contracts | contract	3,918	6,492
Total derivatives, Number of contracts | contract	8,178	17,232
Derivative assets net amount on balance sheet	$ 133	$ 142
Asset derivatives gross amount	133	142
Asset derivatives, gross liability	0	0
Derivative liabilities net amount on balance sheet	(544)	(507)
Total derivatives, fair value, net	(411)	(365)
Liability derivatives, gross asset	25	39
Liability derivatives gross amount	(569)	(546)
Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, notional amount	$ 790	$ 73
Total asset derivatives, number of contracts | contract	4,260	10,740
Derivative assets net amount on balance sheet	$ 133	$ 142
Asset derivatives gross amount	133	142
Asset derivatives, gross liability	$ 0	$ 0
Other assets | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, number of contracts | contract	468	3,668
Currency Swap | Other investments | Derivatives designated as fair value accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, notional amount		$ 2
Derivative assets net amount on balance sheet		0
Asset derivatives gross amount		0
Asset derivatives, gross liability		0
Interest rate cap agreements | Other liabilities & accrued expenses | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total liability derivatives, notional amount	$ 32	34
Derivative liabilities net amount on balance sheet	0	0
Liability derivatives, gross asset	0	0
Liability derivatives gross amount	0	0
Futures | Other assets | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Derivative assets net amount on balance sheet	0	0
Asset derivatives gross amount	0	0
Asset derivatives, gross liability	$ 0	$ 0
Futures | Other liabilities & accrued expenses | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total liability derivatives, number of contracts | contract	556	1,089
Derivative liabilities net amount on balance sheet	$ 0	$ 0
Liability derivatives, gross asset	0	0
Liability derivatives gross amount	$ 0	$ 0
Equity and index contracts | Other liabilities & accrued expenses | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total liability derivatives, number of contracts | contract	2,662	5,400
Derivative liabilities net amount on balance sheet	$ (60)	$ (68)
Liability derivatives, gross asset	0	0
Liability derivatives gross amount	$ (60)	$ (68)
Options | Other investments | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, number of contracts | contract	2,829	5,539
Derivative assets net amount on balance sheet	$ 126	$ 140
Asset derivatives gross amount	126	140
Asset derivatives, gross liability	$ 0	$ 0
Futures | Other assets | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, number of contracts | contract	963	1,533
Derivative assets net amount on balance sheet	$ 1	$ 1
Asset derivatives gross amount	1	1
Asset derivatives, gross liability	$ 0	$ 0
Futures | Other liabilities & accrued expenses | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total liability derivatives, number of contracts | contract	700	3
Derivative liabilities net amount on balance sheet	$ 0	$ 0
Liability derivatives, gross asset	0	0
Liability derivatives gross amount	0	0
Total return swap agreements – fixed income | Other investments | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, notional amount		56
Derivative assets net amount on balance sheet		1
Asset derivatives gross amount		1
Asset derivatives, gross liability		0
Total return swap agreements – fixed income | Other liabilities & accrued expenses | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total liability derivatives, notional amount	80	119
Derivative liabilities net amount on balance sheet	0	0
Liability derivatives, gross asset	0	0
Liability derivatives gross amount	0	0
Total return swap agreements – equity index | Other investments | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, notional amount	7
Derivative assets net amount on balance sheet	0
Asset derivatives gross amount	0
Asset derivatives, gross liability	0
Total return swap agreements – equity index | Other liabilities & accrued expenses | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total liability derivatives, notional amount		187
Derivative liabilities net amount on balance sheet		11
Liability derivatives, gross asset		11
Liability derivatives gross amount		0
Foreign currency forwards | Other investments | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, notional amount	8
Derivative assets net amount on balance sheet	0
Asset derivatives gross amount	0
Asset derivatives, gross liability	0
Foreign currency forwards | Other liabilities & accrued expenses | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total liability derivatives, notional amount	720	745
Derivative liabilities net amount on balance sheet	17	19
Liability derivatives, gross asset	24	28
Liability derivatives gross amount	(7)	(9)
Guaranteed accumulation benefits | Contractholder funds | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total liability derivatives, notional amount	133	161
Derivative liabilities net amount on balance sheet	(21)	(18)
Liability derivatives, gross asset	0	0
Liability derivatives gross amount	(21)	(18)
Guaranteed withdrawal benefits | Contractholder funds | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total liability derivatives, notional amount	188	205
Derivative liabilities net amount on balance sheet	(17)	(14)
Liability derivatives, gross asset	0	0
Liability derivatives gross amount	(17)	(14)
Equity-indexed and forward starting options in life and annuity product contracts | Contractholder funds | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total liability derivatives, notional amount	1,784	1,791
Derivative liabilities net amount on balance sheet	(459)	(430)
Liability derivatives, gross asset	0	0
Liability derivatives gross amount	(459)	(430)
Credit default swaps – buying protection | Other investments | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, notional amount	25	17
Derivative assets net amount on balance sheet	0	0
Asset derivatives gross amount	0	0
Asset derivatives, gross liability	0	0
Credit default swaps – buying protection | Other liabilities & accrued expenses | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total liability derivatives, notional amount	119	152
Derivative liabilities net amount on balance sheet	(4)	(7)
Liability derivatives, gross asset	1	0
Liability derivatives gross amount	(5)	(7)
Credit default swaps – selling protection | Other investments | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, notional amount	750
Derivative assets net amount on balance sheet	6
Asset derivatives gross amount	6
Asset derivatives, gross liability	0
Credit default swaps – selling protection | Other liabilities & accrued expenses | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total liability derivatives, notional amount	9	9
Derivative liabilities net amount on balance sheet	0	0
Liability derivatives, gross asset	0	0
Liability derivatives gross amount	0	$ 0
Other | Other assets | Derivatives designated as fair value accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, notional amount	3
Derivative assets net amount on balance sheet	0
Asset derivatives gross amount	0
Asset derivatives, gross liability	$ 0